1. Field of the Invention
The present invention relates to an image reading device which reads image data on an original while conveying the original, and an image forming apparatus including the reading device.
2. Description of Related Art
Conventionally, an image forming apparatus such as a copy machine includes an image reading device. There has been proposed an image reading device which is capable of reading with a scanning unit staying at a predetermined position while conveying an original fed from an automatic original feeder in the sub scanning direction, and another image reading device which is capable of reading double sides of an original (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. H07-110641).
An image forming apparatus including an image reading device which is capable of reading double sides of an original will now be described with reference to FIG. 5. FIG. 5 is a longitudinal sectional view of an image forming apparatus including a conventional image reading device.
As shown in FIG. 5, the image forming apparatus is provided with an image reading device A that reads image data on an original, and a printing device B that forms the image data read by the image reading device A on a sheet of paper.
The image reading device A is comprised of an auto document feeder (hereinafter referred to “the ADF”) 2 and a scanning device 1. The ADF 2 has an original tray 12, a pick-up roller 43, pairs of separating rollers 44a, 44b, a plurality of conveying rollers 46, 48, discharge rollers 49, and a discharge tray 50. Originals D are stacked on an original tray 12. The originals D stacked on the original tray 12 are separated one by one by the pick-up roller 43 and a pair of the separating rollers 44a, 44b, and conveyed onto a conveying path 156. The original D is conveyed along the conveyance roller 156, and the image on the original D is read by the scanning device 1. The original D is, after the image on the original is read, discharged onto the discharge tray 50 by the conveying rollers 48 and the discharge rollers 49.
An inversion flapper 152 is disposed at a portion downstream of the conveying rollers 48 so as to enable the double sides of the original D to be read. An inversion conveying path 153 is also provided to invert a surface of the original D to be read.
The scanning device 1 has a platen glass 22 and a scanning unit 21 disposed below the platen glass 22. The scanning unit 21 is adapted to move in the direction of an arrow F (the sub scanning direction) in the FIG. 5 being guided by a guide rail 24. The scanning unit 21 is provided with a plurality of lamps 21c which illuminate the original D, a line CCD (Charge Coupled Device) 21g, and an optical system 21f that guides the reflected light from the original illuminated by the respective lamps 21c. 
The image reading device A has two modes; a moving original reading mode and a fixed original reading mode. Reading can be performed in each mode.
In the moving original reading mode, the original D fed from the ADF 2 is read by the scanning unit 21 while being conveyed in the sub scanning direction. Specifically, the original D is fed from the ADF 2, and conveyed in the sub scanning direction. In this case, the scanning unit 21 stays at a moving original reading position 101 facing a moving original reading position 102. When the original D being conveyed in the sub scanning direction passes through the moving original reading position 101, reading of the original D in the main scanning direction is performed by the scanning unit 21, which enables the whole surface of one side of the original D to be read. The original D is discharged onto the discharge tray 50 by the conveying rollers 48 and the discharge rollers 49. Reading one side of the original D is thus performed.
In the moving original reading mode, when the double-sided reading mode is selected, the original D is pulled out of the device by the discharge rollers 49 until its rear part passes through the inversion flapper 152 after one side of the original D is read. Next, when the inversion flapper is switched over, the discharge rollers 49 are rotated in the opposite direction, which causes the original D to be guided to the inversion conveying path 153, with the surface of the original D to be read being inverted. The original D is conveyed again towards the moving original position 101 by the conveyance rollers 46 and the other side of the original D is read by the scanning unit 21. Reading double sides of the original D is thus performed.
On the other hand, in the fixed original reading mode, the original D is placed at a predetermined position on the platen glass 22, and the scanning unit 21 is moved in the sub scanning direction to the placed original D. Namely, the scanning unit 21 is moved in the sub scanning direction relative to the original D on the platen glass 22 while reading the original D in the main scanning direction. Reading the whole of the original is thus performed.
The printing device B has a laser unit 3. The laser unit 3 modulates a laser beam based on the image data (a video signal) read by the image reading device A, and then irradiates the laser beam onto a photosensitive drum 10, thereby allowing an electrostatic latent image to be formed on the photosensitive drum 10. The electrostatic latent image formed on the photosensitive drum 10 is visualized as a toner image with toner provided by a developing unit 11. The toner image is transferred on a sheet P fed via registration rollers 5 from a sheet feeding cassette 4, by a transfer unit 6. The sheet P on which the toner image is transferred is conveyed to a fixing unit 7. This fixing unit 7 fixes the toner image on the sheet P by applying thermal pressure to the sheet P. The sheet P on which the toner image is fixed is discharged onto a discharge tray 9 via discharge rollers 8.
However, since the conventional image reading device A includes the scanning unit 21 mounting the line CCD, the optical system and the like, the construction to realize the moving original reading mode is complicated, thereby making it difficult to realize cost-reduction and miniaturization of the device.
Further, since the inversion flapper 152 to invert the original, the inversion conveying path 153 and the like are needed to realize double-sided reading of the original, the apparatus becomes big and the cost gets high, thereby making it difficult to realize cost-reduction and miniaturization of the device.